Groceries can have expiration dates you might want to check, and produce and fruit quality that varies. Or frozen food that you might not be sure of how long it's been sitting outside of the freezer.
Also, there are so many grocery stores (where I live at least, and in all suburban US areas I've been in), that you must be driving by one at some point in the week. The transportation costs are nil, so the only difference is the time you spend in the grocery store. Which is also very low if you're familiar with the store.
Therefore, the only missing variable is how much you trust the worker that is walking around picking things up, and for me, that is very little, especially if there is a price premium with picking up a grocery order.
Also, there are so many grocery stores (where I live at least, and in all suburban US areas I've been in), that you must be driving by one at some point in the week. The transportation costs are nil, so the only difference is the time you spend in the grocery store. Which is also very low if you're familiar with the store.
Therefore, the only missing variable is how much you trust the worker that is walking around picking things up, and for me, that is very little, especially if there is a price premium with picking up a grocery order.